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March,1929 A.MERICAN CINEMATOGRAPHER Thirty-five
The A. B. C. of Sound Pictures
By JOSEPH A. DUBRAY, A. S. C.
(Continuedjrom Page 29)
felt to express these vibrations in a tangible manner so
that they could be, so to speak, materialized and seen.
Since sound can be heard in all directions around its
source without any change in its quality, it was evident
that the knowledge of the behavior of the sound vibra-tions
emitted by one point of the sound source and reach-ing
one point of the ear should be sufficient for the re-searcher
to reach a complete understanding of all of the
vibrations simultaneously emitted by the same source.
It was inferred that the vibrating source of sound im-parted
a vibratory movement to the nearest particle of
carrying medium, say of air, which in turn would im-part
a similar vibrating movement to the next nearest
particle, and on to the third and fourth and so on until
a certain particle of air would strike the drumhead of
the ear and set it to vibrating.
The shortest distance between two points is graphic-ally
represented by a straight line. It is quite logical to
visualize the disturbance created by a vibratory move-ment
as following a path diverging from the straight line,
but nevertheless traveling in its same direction. This
can .easily be seen by pinching at any point a taut string.
The string vibrates to and fro, although its position re-mains
unchanged.
By visualizing and unjting the subsequent position of
the innumerable air particles successively set to vibrate
and carrying the purest and simplest forms of sound, a
continuous line was obtained having a maximum point on
one side of the straight line uniting the two chosen
points, a maximum on the other side and alternately
crossing it at equal intervals. Such form suggested the
name of curve.
This curve would have a certain amplitude, or distance,
from its peaks to the straight line, and a certain uniform
distance between the peaks and the points crossing the
straight line,
The amplitude expresses the loudness of the sound and
represents the movement to and fro of the particles of
air while the distance between two peaks situated on the
same side of the straight line represent the pitch or the
note which we assign to the sound.
Now, sound vibrations are transmitted from one point
to another with the same velocity, irrespective of their
loudness or pitch. It is then evident that the closer the
peaks of the curve are to each other, the more frequent
will be the impact of these peaks upon the drumhead of
the ear. The number of peaks passing a certain point
during a lapse of time of one second has been termed the
frequency of the vibratory movement and can be meas-ured
with great accuracy.
Similarly LIGHT has been constructed to be due to
vibrations with the difference that its behavior' precludes
the possibility that its vibratory movement can be trans-mitted
by the same media which carry sound.
It was Huyghens who, in 1678, expressed the theo-retical
existence of an elastic, imponderable medium
which he called the ether and which he supposed to exist
everywhere in the Universe, within solids, liquids, gases
and which he surmised filled the interstellar spaces.
Here again a point source of light would be a center
of disturbance; it would successively set into vibration
particles of the ether which, finally entering the eye
would excite its retina and so produce the sensation of
vision. Here again, vibrations were sent forth in all
directions and again the section of such vibrations unit-ing
a point source of light with one point of the receiv-ing
eye, could be graphically represented as a sinuous
continuous curve similar to the imaginary section of the
waves created upon the surface of stagnant water when
it is disturbed by, say, throwing a pebble in it.
This similarity of the line representing light vibra-tions
with the cross section of water waves, has given
rise to the well-known expression of light waves and, by
extension the expression of sound waves, although not-withstanding
the fact that the movement of the latter is
represented by similar lines as the former, it must be
kept ever present in mind that the light waves present,
as water waves, a transverse or up and down movement,
while the disturbance of sound is longitudinal and can be
visualized as being carried flatly upon the surface of the
stagnant water.
It has been previously stated that the transmission of
sound and light occurs through vibrations imparted suc-cessively
to adjacent particles of the transmitting med-ium.
This may be better understood by analyzing the
movements of a floating object, a cork, for example, set
upon the disturbed surface of water. It will be"noticed
that an up and down movement is imparted to the cork
by the water waves though the cork itself does not ad-vance
with the waves.
The apparent longitudinal motion of the waves is then
illusory; their movement is merely a motion of particles
within the mass while the mass remains stationary.
Similarly the light and sound transmitting media do
not actually displace themselves, but vibrations are im-parted
from particle to particle until they reach the ear
or the eye of the listener or observer, whichever the case
may be.
The light waves are characterized, as the sound waves,
by their amplitude and their length, the first of which
determines the brilliance and the second the color of the
light sensation transmitted to the brain.
Although the truth of the undulatory theory for light
has been relatively recently challenged and an electro-magnetic
theory is rapidly gaining favor, the wave theory
holds its popularity because, notwithstanding its simplic-ity,
it permits a scientific explanation of all the phenom-ena
of light such as the phenomena of reflection, of re-fraction,
of interference and of polarization.
When the light of the sun strikes, say, a tree, its leaves
absorb some of the light waves and reflect others, and
these reflected waves are those which reach the eye of
the observer and are of the wave length which charac-terizes
the green color of the leaves. Similarly, the trunk
of the tree will reflect only the light waves which char-acterize
its particular color, while the image of the tree
is formed on the retina by the optical system of the eye.
Thus a perfect image of the tree through the eye is trans-mitted
to the brain and the tree is said to be seen.
Since an object can be seen because it reflects some
particular vibrations of the ether and since a sound can
be heard because it causes the medium into which it
travels to vibrate, it is quite logical to conceive the pos-sibility
of reproducing the visibility of an object or the
audibility of a sound by forcing the ether or the sound
transmitting medium to vibrate in the same form, ampli-tude
and frequency of waves as those which have pro-duced
the original sensation.
Thus a painter, after outlining on canvas the form of
the tree, will apply to the canvas substances (paints)
which reflect only the light waves corresponding to the
green of the leaves or the browns of the trunk in their
proper position and relation, and that painting when
looked at will, at any time, any place, give to the eye the
impression of seeing the tree, the faithfulness of repro-duction
depending, of course, upon the skill of the painter.
PhoneGL. 7507 Hours9 to 5
Dr. G. Floyd Jackman
DENTIST
706HollywoodFirst National Building
HollywoodBlvd.at HighlandAve.
•

March,1929 A.MERICAN CINEMATOGRAPHER Thirty-five
The A. B. C. of Sound Pictures
By JOSEPH A. DUBRAY, A. S. C.
(Continuedjrom Page 29)
felt to express these vibrations in a tangible manner so
that they could be, so to speak, materialized and seen.
Since sound can be heard in all directions around its
source without any change in its quality, it was evident
that the knowledge of the behavior of the sound vibra-tions
emitted by one point of the sound source and reach-ing
one point of the ear should be sufficient for the re-searcher
to reach a complete understanding of all of the
vibrations simultaneously emitted by the same source.
It was inferred that the vibrating source of sound im-parted
a vibratory movement to the nearest particle of
carrying medium, say of air, which in turn would im-part
a similar vibrating movement to the next nearest
particle, and on to the third and fourth and so on until
a certain particle of air would strike the drumhead of
the ear and set it to vibrating.
The shortest distance between two points is graphic-ally
represented by a straight line. It is quite logical to
visualize the disturbance created by a vibratory move-ment
as following a path diverging from the straight line,
but nevertheless traveling in its same direction. This
can .easily be seen by pinching at any point a taut string.
The string vibrates to and fro, although its position re-mains
unchanged.
By visualizing and unjting the subsequent position of
the innumerable air particles successively set to vibrate
and carrying the purest and simplest forms of sound, a
continuous line was obtained having a maximum point on
one side of the straight line uniting the two chosen
points, a maximum on the other side and alternately
crossing it at equal intervals. Such form suggested the
name of curve.
This curve would have a certain amplitude, or distance,
from its peaks to the straight line, and a certain uniform
distance between the peaks and the points crossing the
straight line,
The amplitude expresses the loudness of the sound and
represents the movement to and fro of the particles of
air while the distance between two peaks situated on the
same side of the straight line represent the pitch or the
note which we assign to the sound.
Now, sound vibrations are transmitted from one point
to another with the same velocity, irrespective of their
loudness or pitch. It is then evident that the closer the
peaks of the curve are to each other, the more frequent
will be the impact of these peaks upon the drumhead of
the ear. The number of peaks passing a certain point
during a lapse of time of one second has been termed the
frequency of the vibratory movement and can be meas-ured
with great accuracy.
Similarly LIGHT has been constructed to be due to
vibrations with the difference that its behavior' precludes
the possibility that its vibratory movement can be trans-mitted
by the same media which carry sound.
It was Huyghens who, in 1678, expressed the theo-retical
existence of an elastic, imponderable medium
which he called the ether and which he supposed to exist
everywhere in the Universe, within solids, liquids, gases
and which he surmised filled the interstellar spaces.
Here again a point source of light would be a center
of disturbance; it would successively set into vibration
particles of the ether which, finally entering the eye
would excite its retina and so produce the sensation of
vision. Here again, vibrations were sent forth in all
directions and again the section of such vibrations unit-ing
a point source of light with one point of the receiv-ing
eye, could be graphically represented as a sinuous
continuous curve similar to the imaginary section of the
waves created upon the surface of stagnant water when
it is disturbed by, say, throwing a pebble in it.
This similarity of the line representing light vibra-tions
with the cross section of water waves, has given
rise to the well-known expression of light waves and, by
extension the expression of sound waves, although not-withstanding
the fact that the movement of the latter is
represented by similar lines as the former, it must be
kept ever present in mind that the light waves present,
as water waves, a transverse or up and down movement,
while the disturbance of sound is longitudinal and can be
visualized as being carried flatly upon the surface of the
stagnant water.
It has been previously stated that the transmission of
sound and light occurs through vibrations imparted suc-cessively
to adjacent particles of the transmitting med-ium.
This may be better understood by analyzing the
movements of a floating object, a cork, for example, set
upon the disturbed surface of water. It will be"noticed
that an up and down movement is imparted to the cork
by the water waves though the cork itself does not ad-vance
with the waves.
The apparent longitudinal motion of the waves is then
illusory; their movement is merely a motion of particles
within the mass while the mass remains stationary.
Similarly the light and sound transmitting media do
not actually displace themselves, but vibrations are im-parted
from particle to particle until they reach the ear
or the eye of the listener or observer, whichever the case
may be.
The light waves are characterized, as the sound waves,
by their amplitude and their length, the first of which
determines the brilliance and the second the color of the
light sensation transmitted to the brain.
Although the truth of the undulatory theory for light
has been relatively recently challenged and an electro-magnetic
theory is rapidly gaining favor, the wave theory
holds its popularity because, notwithstanding its simplic-ity,
it permits a scientific explanation of all the phenom-ena
of light such as the phenomena of reflection, of re-fraction,
of interference and of polarization.
When the light of the sun strikes, say, a tree, its leaves
absorb some of the light waves and reflect others, and
these reflected waves are those which reach the eye of
the observer and are of the wave length which charac-terizes
the green color of the leaves. Similarly, the trunk
of the tree will reflect only the light waves which char-acterize
its particular color, while the image of the tree
is formed on the retina by the optical system of the eye.
Thus a perfect image of the tree through the eye is trans-mitted
to the brain and the tree is said to be seen.
Since an object can be seen because it reflects some
particular vibrations of the ether and since a sound can
be heard because it causes the medium into which it
travels to vibrate, it is quite logical to conceive the pos-sibility
of reproducing the visibility of an object or the
audibility of a sound by forcing the ether or the sound
transmitting medium to vibrate in the same form, ampli-tude
and frequency of waves as those which have pro-duced
the original sensation.
Thus a painter, after outlining on canvas the form of
the tree, will apply to the canvas substances (paints)
which reflect only the light waves corresponding to the
green of the leaves or the browns of the trunk in their
proper position and relation, and that painting when
looked at will, at any time, any place, give to the eye the
impression of seeing the tree, the faithfulness of repro-duction
depending, of course, upon the skill of the painter.
PhoneGL. 7507 Hours9 to 5
Dr. G. Floyd Jackman
DENTIST
706HollywoodFirst National Building
HollywoodBlvd.at HighlandAve.
•